Fuel tank vent system

ABSTRACT

An apparatus and method vent a fuel tank through an oleophobic membrane. In one embodiment, a pressure relief valve accommodates pressure buildups that may result from use of the oleophobic membrane. In one embodiment, a vacuum relief valve accommodates pressure drops within the fuel tank. that may result from use of the oleophobic membrane.

BACKGROUND

Fuel tanks are often vented. However, liquid fuel sometimes undesirablyenters the vent system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a fuel tank vent system accordingto an example embodiment.

FIG. 2 is a schematic illustration of another embodiment of the fueltank vent system of FIG. 1.

FIG. 3 is a schematic illustration of another embodiment of the fueltank vent system of FIG. 1 according to an example embodiment.

FIG. 4 is a schematic illustration of another embodiment of the fueltank vent system of FIG. 1 according to an example embodiment.

FIG. 5 is a draft illustrating operational characteristics of the fueltank vent system of FIG. 4 according to an example embodiment.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

FIG. 1 schematically illustrates a fuel tank vent system 10 according toan example embodiment. As will be described hereafter, fuel tank ventsystem 10 vents a fuel tank through an oleophobic membrane whichinhibits liquid fuel from entering the vent system. Fuel tank ventsystem can further includes one or both of a carburetor and a pressurerelease valve that accommodate pressure buildups while a vacuum reliefvalve accommodates pressure drops within the fuel tank that may resultfrom use of the oleophobic membrane.

Fuel tank vent system 10 includes fuel tank 12, vent conduits 14A, 14B(collectively referred to as vent conduits 14), membranes 16A, 16B(collectively referred to as membrane 16), vapor system 18, fuel pump20, carburetor 22 of fuel intake system 24, pressure relief valve 28 andvacuum relief valve 30. Fuel tank 12 comprises a tank configured tocontain and supply fuel for use by an internal combustion engine havingintake system 24. In one embodiment, fuel tank 12 comprises a plasticfuel tank. In other embodiments, fuel tank 12 may be formed from othermaterials.

Vent conduits 14 comprise openings within or passages extending fromfuel tank 12 through which an interior of the fuel tank 12 is vented.Vent conduits 14 communicate with an interior of fuel tank 12 proximateto a top side of fuel tank 12, allowing fuel vapors to rise and passthrough vent conduits 14. Vent conduits 14 direct vapors from fuel tank12 to membranes 16.

Although system 10 is illustrated as including two vent conduits 14, inother embodiments, system 10 may include a single vent conduit 14 ormore than two vent conduits 14. In one embodiment, vent conduits 14comprise tubes extending from fuel tank 12 to membranes 16. In anotherembodiment, vent conduits 14 merely comprise openings within fuel tank12, wherein membranes 16 are located within the openings and within thewalls around the openings in fuel tank 12.

Membranes 16 comprise oleophobic membranes configured to allow the flowof vapors or gases therethrough while preventing or inhibiting the flowor movement of fuel and other liquids across such membranes. Membranes16 have high gas permeabilities while repelling liquids. Membranes 16extend between fuel tank 12 and vapor system 18 to inhibit fuel fromentering vapor system 18 while permitting gases or vapors to pass tovapor system 18. Although system 10 is illustrated as including twomembranes 16, in other embodiments, system 10 may include a singlemembrane 16 or more than two membranes 16.

In one embodiment, membranes 16 each comprise a filter medium substratetreated with a coating material including a cross-linkedfluorosulfone-containing oligomer, which coats the surface of thesubstrate. This coating provides permanent oleophobicity andhydrophobicity to the filter. Examples of the material from whichmembrane 16 may be provided are found in U.S. Pat. No. 6,579,342 issuedon Jun. 17, 2003 to Wang et al., the full disclosure of which is herebyincorporated by reference. In other embodiments, membranes 16 may beprovided by other hydrophobic or oleophobic filters or materials.

Vapor system 18 comprises one or more mechanisms configured to inhibitor reduce the extent to which vapors are released to atmosphere. In oneembodiment, vapor system 18 comprises one or more carbon canistersconfigured to collect and store hydrocarbons for later use or disposal.In another embodiment, vapor system 18 comprises one or more conduitswhich direct vapors back to fuel intake system 24 where the hydrocarbonsare consumed. For example, in one embodiment, such conduits directhydrocarbons back to an upstream side of carburetor 22. In someembodiments, vapor system 18 may additionally include one or morefilters for filtering predetermined vapor components, wherein somepredetermined vapor components, such as hydrocarbons, are redirected forstorage or consumption and wherein other predetermined vapor componentsare permitted to be released to atmosphere. In some embodiments, vaporsystem 18 may have other configurations for filtering, consuming and/orstoring vapors from fuel tank 12.

Fuel pump 20 comprises a fuel pump operatively coupled between fuel tank12 and fuel intake system 24 so as to pump or pressurize the flow offuel from tank 12 to intake system 24. Fuel pump 20 increases the flowof fuel from fuel tank 12 to overcome the otherwise restriction of fuelflow that may occur when membranes 16 become fuel wetted. In someembodiments, fuel pump 20 may be omitted.

Carburetor 22 is part of fuel intake system 24 and is configured toblend air and fuel from fuel tank 12 for use by an internal combustionengine including fuel intake system 24. As compared to internalcombustion engines without membranes 16, carburetor 22 is configured torestrict intake of fuel to fuel intake system 24. In particular,carburetor 22 may have a smaller bowl inlet needle valve seat diameterto counteract high fuel supply pressures that may occur when membranes16 become fuel wetted. In yet other embodiments, where fuel intakesystem 24 is part of a fuel injection system, carburetor 22 may beomitted.

Pressure relief valve 28 comprises a valve mechanism in pneumaticcommunication with an interior of fuel tank 12 which is configured torelieve or lessen pressure within an interior of tank 12 when pressureswithin tank 12 exceed a predetermined threshold. Pressure relief valve28 inhibit excess pressure build up within fuel tank 12 which mightoccur during fuel heating on warm-up, during wetting of membrane 16 andduring diurnal heating. Pressure relief valve 28 inhibit pressurebuildups within fuel tank 12 that might otherwise damage, deform orexpand tank 12 to an undesirable extent, such as when fuel tank 12comprises a plastic fuel tank. For example, pressure relief valve 28 mayprevent undesirable expansion of fuel tank 12 into contact with a hotpart of an engine which might melt or damage fuel tank 12. Pressurerelief valve 28 may additionally inhibit excessive pressurization offuel being delivered to fuel intake system 24 such that a proper flowrate of fuel to fuel intake system 24 is achieved. Nominally thepressure relief valve 28 is closed forcing fuel tank vapors throughvapor system 18.

Vacuum relief valve 30 comprises a valve mechanism in pneumaticcommunication with an interior of fuel tank 12 which is configured torelieve or lessen vacuum within an interior of tank 12 when the vacuumwithin tank 12 exceeds a predetermined threshold. Vacuum relief valve 30inhibits excess vacuum within fuel tank 12 which might otherwise damage,deform or contract tank 12 to an undesirable extent, such as when fueltank 12 comprises a plastic fuel tank. Vacuum relief valve 30counteracts any vacuum that may occur during fuel use or diurnal tankcooling. In one embodiment, vacuum relief valve 30 is configured tolimit vacuum within fuel tank 12 to less than three inches of watervacuum relative to atmosphere. In some embodiments, vacuum relief valve30 may be omitted.

As schematically shown in FIG. 1, in the example illustrated, pressurerelief valve 28 and vacuum relief valve 30 are both incorporated intoand as part of a fuel tank cap 34. For example, 34, which includes valve28 and 30, may screw or otherwise fit into a fill opening 36 throughexterior walls of fuel tank 12 so as to close off the fill opening 36 offuel tank 12. Cap 30 is configured to be removed or separated from fueltank 12, allowing fuel to be filled into fuel tank 12, and then laterreattached to fuel tank 12 covering the fill opening 36. As a result,the construction of fuel tank 12 is simplified and repair, replacementby subsequent addition of cap 34 including valve 28 and 30 isfacilitated.

In other embodiments, pressure relief valve 28 may alternatively beincorporated into a wall of fuel tank 12. In other embodiments, thevacuum relief valve 30 may be incorporated as part of a wall of fueltank 12. In yet other embodiments, both pressure relief valve 28 andvacuum relief valve 30 may be provided in a wall of fuel tank 12 ratherthan being incorporated into cap 34. In yet other embodiments, pressurerelief valve 28 and vacuum relief valve 30 may be provided as part of asingle valve mechanism which relieves pressure within fuel tank 12 at apredetermined pressure threshold within tank 12 and which also relievesvacuum within fuel tank 12 at a predetermined vacuum threshold withintank 12. For example, in one body, pressure relief valve 28 and vacuumrelief valve 30 may be provided as part of a single duck bill umbrellavalve mechanism.

Overall, fuel tank vent system 10 collects or consumes fuel vapors. Oneor both of a carburetor and a pressure release valve accommodatepressure buildups while a vacuum relief valve accommodates pressuredrops within the fuel tank that may result from use of the oleophobicmembrane. As a result, fuel tank vent system 10 counteracts negativeside effects of such membranes 16 to prevent damage to fuel tank 12 andensure proper fuel flow to the fuel intake system 24.

FIG. 2 schematically illustrates fuel tank vent system 110, anotherembodiment of fuel tank vent system 10. Fuel tank vent system 110 issimilar to fuel tank vent system 10 except that fuel tank vent system110 includes carbon canister 118, vacuum relief valve 130 and cap 134 inplace of vapor system 18, vacuum relief valve 30 and cap 34,respectively. Those remaining components of fuel tank vent system 110which correspond to components of fuel tank vent system 10 are numberedsimilarly.

Carbon canister 118 comprises a particular embodiment of vapor system18. Carbon canister 118 comprises one or more carbon collectioncanisters or containers configured to collect and store hydrocarbons forlater use or disposal. Carbon canister 118 receives hydrocarbon vaporsthat have passed through membranes 16. In other embodiments, carboncanister 118 may comprise other vapor collection and/or consumptionmechanisms.

Vacuum relief valve 130 and cap 134 are similar to vacuum relief valve30 and cap 34 except that vacuum relief valve 130 is not incorporated aspart of cap 134, but is instead incorporated as part of wall 138 of fueltank 12. Cap 134 merely includes pressure relief valve 28. Vacuum reliefvalve 130 and pressure relief valve 28 perform similar functions asthose performed by pressure relief valve 28 and vacuum relief valve 30described above.

FIG. 3 schematically illustrates fuel tank vent system 210, anotherembodiment of fuel tank vent system 10. Fuel tank vent system 110 issimilar to fuel tank vent system 10 except that fuel tank vent system110 includes vapor return conduit 218, pressure relief valve 228, vacuumrelief valve 230 and cap 234 in place of vapor system 18, pressurerelief valve 28, vacuum relief valve 30 and cap 34, respectively. Thoseremaining components of fuel tank vent system 110 which correspond tocomponents of fuel tank vent system 10 are numbered similarly.

Vapor return conduit 218 comprises a particular embodiment of vaporsystem 18. Vapor return conduit 218 comprises one or more conduitsconfigured to direct vapors back to fuel intake system 24 where thehydrocarbons are consumed. For example, in one embodiment, such conduitsdirect hydrocarbons back to an upstream side of carburetor 22. In someembodiments, vapor system 18 may additionally include one or morefilters for filtering predetermined vapor components, wherein somepredetermined vapor components, such as hydrocarbons, are redirected forconsumption and wherein other predetermined vapor components arepermitted to be released to atmosphere or are directed to collectioncanisters. In some embodiments, vapor system 218 may have otherconfigurations for filtering, consuming and/or storing vapors from fueltank 12.

Pressure relief valve 228, vacuum relief valve 230 and cap 134 aresimilar to pressure relief valve 28, vacuum relief valve 30 and cap 34except that pressure relief valve 228 and vacuum relief valve 230 arenot incorporated as part of cap 234, but are instead incorporated aspart of wall 138 of fuel tank 12. Pressure relief valve 228 and vacuumrelief valve 130 perform similar functions as those performed bypressure relief valve 28 and vacuum relief valve 30 described above.

FIG. 4 schematically illustrates fuel tank vent system 310, anotherembodiment of fuel tank vent system 210. Fuel tank vent system 310 isidentical to fuel tank vent system 210 except that fuel tank vent system310 is specifically illustrated as having a fuel tank 312 including afill tube or fill neck 313. Fill neck 313 comprises a tube extending toa predetermined location or depth into an interior of fuel tank 212.Fill neck 313 assists in regulating the filling of tank 312 to inhibitover-filling of tank 312.

FIG. 5 is a graph or chart illustrating venting characteristics ofpressure relief valve 228 and vacuum relief valve 230 when incorporatedinto fuel tank vent system 310. As shown by area 400, vacuum reliefvalve 230 is configured to vent air or gas into tank 312 at a flow rategreater than or equal to a maximum anticipated fuel consumption rate forthe engine being supplied with fuel (F_(fcmax)). In the exampleillustrated, vacuum relief valve 230 vents air into tank 312 at a flowrate of at least 25 cubic centimeters per minute (ccm or sccm). As aresult, vacuum relief valve 230 accommodates any vacuum that may resultfrom an airflow restriction resulting from use of the oleophobic duringstart up of the engine so as to maintain a desired air to fuel ratio inthe fuel being supplied to the engine.

As shown by area 402, pressure relief valve 228 is configured to ventout gas from the interior of fuel tank 312 during filling of tank 312with fuel. Pressure relief valve 228 is configured to send out gas at aflow rate of no greater than V/T, wherein V is a volume of the fill neck313 and wherein T is the desired recession time for a given capacity oftank 312 (the desired amount of time for fuel within fuel neck 3132 torecede when a desired percentage of the interior of the fuel tank 312has been filled with fuel). Pressure relief valve 230 releases or ventsgas from tank 312 at a maximum rate of V/T until the pressure withintank 312 attains a pressure of P_(n). Pressure P_(n) is the neck headpressure or the distance between a rim of filler neck 313 and a desiredfill capacity (nominally in a range from 2-6 inches). In the exampleillustrated, pressure relief valve 228 is configured to vent out gasfrom the interior of the fuel tank at a flow rate of between about 30ccm and 170 ccm up to a pressure within the interior of the tank of 1.2KPa. As a result, pressure relief valve 228 cooperates with fill neck313 to provide a user with a positive indication of when fuel tank 312is filled to its desired fill capacity, accommodating pressure changesresulting from membranes 16.

As shown by area 404, pressure relief valve 228 is further configured tovent vapors or gas from the interior of tank 312 at pressures exceedingP_(n). As shown by area 406, when the pressure within tank 312 reaches apressure which the air to fuel ratio being supplied to the engine isdetrimentally impacted, pressure relief valve 228 vents gas at a flowrate of at least F_(TMmax) starting at a maximum pressure within theinterior of the tank (P_(AFI)) that causes the air to fuel ratio to lieoutside the air to fuel ratio operating range of the engine beingsupplied with fuel. In the example illustrated, the flow rate F_(TMmax)is greater than or equal to a rate at which pressure increases withinthe interior from thermal expansion and motion generated vapors. As aresult, pressure relief valve 228 accommodates pressure increases thatmay result from membranes 16 (shown in FIG. 3) to maintain anappropriate air to fuel ratio of the fuel being supplied to the enginefrom fuel tank 12.

Although the present disclosure has been described with exampleembodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the claimed subject matter. For example, although different exampleembodiments may have been described as including one or more featuresproviding one or more benefits, it is contemplated that the describedfeatures may be interchanged with one another or alternatively becombined with one another in the described example embodiments or inother alternative embodiments. Because the technology of the presentdisclosure is relatively complex, not all changes in the technology areforeseeable. The present disclosure described with reference to theexample embodiments and set forth in the following claims is manifestlyintended to be as broad as possible. For example, unless specificallyotherwise noted, the claims reciting a single particular element alsoencompass a plurality of such particular elements.

1. An apparatus comprising: a fuel tank; a vent conduit extending froman interior of the fuel tank; an oleophobic membrane across the ventconduit; and a vacuum relief valve between the interior of the fuel tankand atmosphere.
 2. The apparatus of claim 1 further comprising apressure relief valve between the interior of the tank and atmosphere.3. The apparatus of claim 2, wherein the pressure relief valve isconfigured to vent out gas from the interior of the fuel tank at a flowrate of between about 30 ccm and 170 ccm up to a pressure within theinterior of the tank of 1.2 KPa.
 4. The apparatus of claim 3, whereinthe fuel tank is configured to supply fuel to an engine configured tooperate using an air to fuel ratio within an intended range and whereinthe pressure relief valve is configured to vent gas out of the interiorof the tank at a flow rate of at least F_(TMmax) starting at a maximumpressure within the interior of the tank that causes the air to fuelratio to lie outside the intended range and wherein the flow rateF_(TMmax) is greater than or equal to the rate of thermal and vaporexpansion within the fuel tank due to increasing thermal transients andmotion generated vapors.
 5. The apparatus of claim 2 further comprisinga cap incorporating the pressure relief valve.
 6. The apparatus of claim5, wherein the cap incorporates the vacuum relief valve.
 7. Theapparatus of claim 1 further comprising a fuel tank incorporating thepressure relief valve.
 8. The apparatus of claim 7, wherein the capincorporates the vacuum relief valve.
 9. The apparatus of claim 1,wherein the cap incorporates the vacuum relief valve.
 10. The apparatusof claim 1, wherein the fuel tank has an outer wall incorporating thevacuum relief valve.
 11. The apparatus of claim 1, wherein the vacuumrelief valve is configured to vent gas into the interior of the fueltank at a flow rate of at least 25 ccm.
 12. The apparatus of claim 1further comprising: a second that conduit influence communication withthe interior of the fuel tank; and a second oleophobic membrane acrossthe second vent conduit.
 13. The apparatus of claim 1 further comprisinga carbon canister connected to the vent conduit on an opposite side ofthe oleophobic membrane as the fuel tank.
 14. The apparatus of claim 1,wherein the vent conduit is connected to an intake system of an engineincluding the carburetor.
 15. An apparatus comprising: a fuel tank; avent conduit extending from an interior of the fuel tank; an oleophobicmembrane across the vent conduit; a pressure relief valve in fluidcommunication with the interior of the tank; and a vacuum relief valvebetween the interior of the fuel tank and atmosphere.
 16. The apparatusof claim 15, wherein the pressure relief valve is configured to vent outgas from the interior of the fuel tank at a flow rate of between about30 ccm and 170 ccm up to a pressure within the interior of the tank of1.2 KPa.
 17. The apparatus of claim 15, wherein the fuel tank isconfigured to supply fuel to an engine configured to operate using anair to fuel ratio within a range and wherein the pressure relief valveis configured to vent gas out of the interior of the tank at a flow rateof at least F_(TMmax) starting at a maximum pressure within the interiorof the tank that causes the air to fuel ratio to lie outside the rangeand wherein the flow rate F_(TMmax) is greater than or equal to the rateof thermal and vapor expansion within the fuel tank due to increasingthermal transients and motion generated vapors.
 18. The apparatus ofclaim 15 further comprising a carburetor operatively coupled to the fueltank and a fuel pump operatively coupled between the fuel tank and thecarburetor.
 19. The apparatus of claim 15 further comprising a capincorporating at least one of the pressure relief valve and the vacuumrelief valve.
 20. A method comprising: venting an interior of a fueltank across an oleophobic membrane to a vapor handling system; andrelieving a vacuum in the fuel tank through a vacuum relief valve.